The frequency range that is reserved worldwide for mobile communication systems comprises many frequency bands. There are a multiplicity of different mobile communication standards and many duplexing methods that a modern mobile communication device needs to be able to use in order to be competitive. At the same time, there is the trend toward ever more advanced miniaturization of electrical components that are installed in mobile communication devices and that use the standards and duplexing methods.
Usual mobile communication standards in Europe are GSM (Global System for Mobile communication) and UMTS (Universal Mobile Telecommunications Systems). Popular duplexing methods are FDD (Frequency Division Duplexing) methods, which involve transmitted and received signals being transmitted simultaneously in principle, but on different frequencies, TDD (Time Division Duplexing) methods, which involve transmitted and received signals being transmitted alternately in successive timeslots, and the duplexing method of the GSM standard, which involves transmitted and received signals being transmitted both on different frequencies and successively in timeslots.
Although the design is meant to be as small as possible, a mobile communication device can therefore easily have ten or more RF filters, even if, e.g., German patent document DE 100 53 205 A1, also published as counterpart U.S. Pat. No. 7,142,884 B2, discloses measures for integrating circuit elements for multiband and/or multimode operation.
The consequences of these contrary trends are an ever greater risk from crosstalk, i.e., the coupling of interfering signals on one signal path into another signal path, and higher costs as a result of more complex circuitry.